Current turbo purge systems use a venturi vacuum generator (such as a vacuum pump) to allow purge of the evaporative system while the turbocharger unit is activated (i.e., the intake manifold is under positive pressure). This vacuum pump often uses significant amounts of the pressurized air created by the turbocharger unit, thereby reducing the power increase created by the turbocharger unit. In order to limit the amount of turbo air running through the pump, and temporarily maximize engine power, a turbo bypass switching valve (BSV) has been used to alter the amount of flow going to the vacuum pump (venturi nozzle).
Recent changes in the legislation of evaporative emissions management systems have required that the On-Board Diagnostic (OBD) system have the capacity to determine if the outlet flow of the venturi (which contains hydrocarbons) is connected to the vehicle inlet system, or if it has become disconnected or broken.
To provide compliance with these regulations, various systems typically require a separate (OBD) relief valve to conduct the OBD test, and detect if there is a leak, or if one or more of the hoses has become disconnected. The valve is necessary to conduct the OBD test. However, the inclusion of this valve adds complexity and cost to the system.
Other attempts to comply with the regulations include systems with the turbo BSV mounted in-line and upstream of the vacuum pump. The drawback to this approach is that this results in an increase in the temperature and pressure requirements for the turbo BSV. Also, the OBD check for every hose connection is more complex and may require additional components.
Accordingly, there exists a need for a valve assembly which is incorporated into the airflow system which is capable of performing the OBD test for failure, as well as having the capability to perform purge system function.